Our invention relates to a method or process for depositing an adherent silver film.
The deposition of metallic films on nonconducting substrates occurs in a conventional manner by wet chemistry methods, in which the component to be metallized is treated with a specially formulated cleaning, etching, conditioning, activating and metallizing bath for a substrate. After cleaning and conditioning next the surface is treated to form nuclei with a noble metal-containing solution and after that metallized according to a conventional process or method.
The treatment baths are usually aqueous solutions containing however an organic solvent component. Disadvantageously this formula for the treatment bath has a high toxicity with considerable volatility of the compounds used, which presupposes corresponding safety precautions.
A further disadvantage of the wet chemistry process is that relatively complex treatment procedures are provide before metallization to achieve the desired adherence. In each case the technical process parameters, such as temperature and treatment time are maintained within narrow limits so that an extensive process control of the process conditions is necessary. The danger of contamination of the treatment bath and process-required fluctuations is large and can clearly cause fluctuations in the quality of the product. The reactivity of the treatment solution itself acts to reduce the quality of a covering lacquer or foil.
Also disadvantageous is the large expense for waste water treatment of the numerous bath solutions and rinses, since many strong etching or heavy metal-containing electrolytes are used.
Especially onerous is the disadvantageous requirement that extensive process adjustments are necessary when different type substrates are to be metallized. The applicable range of a particular wet chemistry process is so narrow under certain conditions that considerable process changes are required when different filler material is used in an organic polymer substrate. A carry-over of process parameters from one material to be coated to another is in any case not possible with a wet chemistry metallization method.
Another known deposition and/or coating method involves thermal decomposition of volatile compounds. This method presupposes very high substrate temperatures of at least 200.degree. C. to 1000.degree. C., which however may be attained for many materials not or only under the danger of material damage.